Patent application title: Mechanically Reinforcing Complex Which is Intended to be Incorporated into a Composite Part and Method of Producing One Such Part

Abstract:

Mechanically reinforcing complex (3), intended for incorporation in a
composite part (1) with injected resin based core (2), comprising a
reinforcing textile structure (5), for impregnation in a thermoset resin
conferring mechanical properties.
It is characterized in that it comprises a layer of open-cell foam (4),
present on the inner face of the complex (3), intended to come into
contact with the resin of the injected core (2).

Claims:

1. Mechanically reinforcing complex (3), intended for incorporation in a
composite part (1) with injected resin based core (2), comprising a
reinforcing textile structure (5), for impregnation in a thermoset resin
conferring mechanical properties, characterized in that it comprises a
layer of open-cell foam (4), present on the inner face of the complex
(3), intended to come into contact with the resin of the injected core
(2).

2. Reinforcing complex according to claim 1, characterized in that the
reinforcing textile structure is a fibrous layer (5).

3. Reinforcing complex according to claim 1, characterized in that the
reinforcing textile structure (10) is an assembly of a plurality of
fibrous layers (11-13).

4. Reinforcing complex according to either of claims 2 and 3,
characterized in that the fibrous layer (5) is based on glass, carbon or
aramid fibres, separate or combined.

5. Reinforcing complex according to claim 1, characterized in that the
foam layer (4) and the reinforcing textile structure (5) are joined by
stitching/knitting.

6. Reinforcing complex according to claim 1, characterized in that the
foam layer and the reinforcing textile structure are joined by needling.

7. Reinforcing complex according to claim 1, characterized in that the
foam layer and the reinforcing textile structure are joined by
non-uniform bonding.

8. Reinforcing complex according to claim 1, characterized in that the
foam layer is based on polyurethane.

9. Reinforcing complex according to claim 1, characterized in that it
comprises a film inserted between the open cell foam layer and the
reinforcing textile structure layer.

10. Method for fabricating a composite part, including an injected resin
based core combined with a reinforcing structure impregnated with a
thermoset resin conferring mechanical properties (mechanizing),
characterized in that it comprises the following steps:placement in a
mould (20) of a complex (3) comprising the textile reinforcing structure
(5) combined with an open cell foam layer (4);injection into the mould of
the components (22,23) reacting to produce a resin (24) forming the core
(2) and coming into contact with the open cell foam layer (4) of the
complex (3);impregnation of the textile reinforcing structure (5) by
injecting a mechanizing resin (31).

11. Method according to claim 10, characterized in that the injection of
the mechanizing resin (31) takes place in the mould into which the
components forming the resin of the core have been injected.

12. Method according to claim 10, characterized in that the injection of
the mechanizing resin (31) takes place in a different mould (30) from the
mould (28) in which the core has been formed.

13. Method according to claim 10, characterized in that between the
formation of the core and the injection of the mechanizing resin, the
mould is opened for placing supplementary layers above the reinforcing
structure.

14. Composite part produced by the method according to one of claims 1 to
13, in which the resin of the core (2) partially penetrates into the open
cell foam layer (4) of the mechanically reinforcing complex.

Description:

TECHNICAL FIELD

[0001]The invention relates to the field of technical textiles, and more
particularly textiles for use as reinforcements for the fabrication of
composite parts. It relates more particularly to a mechanically
reinforcing complex used in the context of methods for producing thick
parts, comprising a core based on injected resin.

[0002]The invention relates more specifically to the particular
constitution of such a complex, which serves to improve the mechanical
properties of the composite part, and particularly in terms of resistance
to delamination, thanks to an equally original method.

PRIOR ART

[0003]In general, composite parts are used in many applications. They are
appreciated for their properties of mechanical strength combined with
very low density. By way of example, mention can be made of the
preparation of various panels used in the field of the construction of
maritime or automotive vehicles, for example for producing parts of
ships' hulls, or even walls of end gates of truck trailers.

[0004]Such parts therefore frequently include the combination of a core
having a relatively high thickness, on which a reinforcing textile
structure is placed, generally impregnated with a thermoset resin
conferring mechanical properties (mechanizing). In practice, the
construction of such a part initially requires the preparation of the
core. This core is frequently prepared on the basis of a polyurethane
resin, appreciated for its mechanical properties, combined with
relatively low density, about 30 to 70 kg/m3. This core is then
sanded to its final shape, and then covered on its outer face with a
reinforcing textile structure, typically based on high toughness fibres,
such as glass, carbon or aramid.

[0005]This textile reinforcing structure is then impregnated with a
mechanizing resin, such as in particular resins of unsaturated polyesters
commonly called "UP" for "unsaturated polyester", or epoxy resins. After
curing, this resin, which deeply impregnates the textile structure,
thereby confers additional stiffness to the composite part. It is
understandable that the sequence of the various steps demands delicate
handling operations, so that it is advisable to eliminate the operation
of bonding the reinforcement to the core.

[0006]One commonly employed solution is to carry out the injection of the
polyurethane foam forming the core, in a mould whereof one of the sides
has previously received the reinforcing textile structure. However, a
problem arises during the injection of the polyurethane resin, because
the said resin, which is injected under pressure, tends to penetrate into
the reinforcing textile structure. Hence, the said structure can no
longer be impregnated by the thermoset mechanizing resin, and therefore
to the detriment of the mechanical properties of the composite part.

[0007]To solve this problem, the Applicant proposed in document EP 1 365
055, the use of reinforcing structures comprising an elastomer layer,
combined with a textile structure. This elastomer layer performs a
barrier function, and prevents the polyurethane foam from penetrating
into the textile reinforcing structure, which thereby preserves its
capacity to be impregnated by the thermoset mechanizing resin. However,
this solution has a number of drawbacks in terms of mechanical strength.
This is because the presence of a sealed barrier layer constitutes a
mechanical discontinuity, which therefore forms an area of embrittlement
in which the risks of delamination may be high.

[0008]Another solution has also been proposed to avoid the operations of
sanding of a prefabricated core. Thus, document FR-2 149 427 describes a
method consisting in the use of a complex combining a textile
reinforcement with a foam layer impregnated with a mechanizing resin.
This complex is placed in the mould, with the foam layer forming a
reservoir of mechanizing resin guided towards the interior of the future
core. After injection of the components reacting to produce the resin of
the core, the expansion of the said resin causes a crushing of the
impregnated foam layer. This compression of the foam expels the
mechanizing resin which impregnated the foam, and in consequence,
impregnates the textile reinforcement in contact with the mould walls.
This method, although having the advantage of limiting the number of
operations and handlings, nevertheless has serious drawbacks in terms of
stiffness of the final part. In fact, when they are placed in the mould,
the textile reinforcement and the resin impregnated foam layer are
independent, and, after migration of the resin, their interface zones
remain an area where the risks of delamination are high. The same applies
to the interface zone between the core resin and the foam layer
impregnated with the mechanizing resin.

[0009]The same problems are observed with the method described in document
U.S. Pat. No. 5,112,663, in which the foam loaded with mechanizing resin
is dried by the pressure applied during the closure of the mould, between
the lid of the mould and the prefabricated core. It may also be observed
that these mechanisms of resin migration and diffusion by mechanical
depression do not serve to guarantee perfect uniformity of the resin
concentration over the whole surface of the composite part.

[0010]It is one object of the invention to permit the production of
reinforced composite parts while limiting the handling steps.

[0011]It is a further object of the invention to improve the delamination
resistance of composite parts incorporating reinforcing textile
structures, and intended to be impregnated with a mechanizing resin.

SUMMARY OF THE INVENTION

[0012]The invention therefore relates to a mechanically reinforcing
complex. Such a complex is intended to be incorporated in a composite
part based on injected resin. This complex comprises, in a manner known
per se, a reinforcing textile structure, which is intended to be
impregnated with a thermoset mechanizing resin, for example based on
unsaturated polyester or epoxy resin.

[0013]According to the invention, this reinforcing complex is
characterized in that it comprises a layer of open cell foam, present on
the inner face of the complex, that is the face intended to come into
contact with the injected foam.

[0014]In other words, the reinforcing complex includes a foam layer which
has a certain permeability to the injected foam, which constitutes the
core of the composite part. Thanks to this controlled permeability, the
reinforcing complex is intimately combined with the core during the
fabrication thereof. In fact, the injected foam of the core penetrates
into the foam layer during the injection, thereby anchoring it, and hence
anchoring the reinforcing complex, with regard to the core. In other
words, during its formation, the core partially penetrates into the
reinforcing complex, and more precisely, of the characteristic foam
layer.

[0015]This characteristic foam is selected to have an optimized porosity
with regard to the resin of the core. This porosity is in fact selected
to ensure limited penetration of this injection resin, in order to
prevent the said resin from impregnating the textile structure that is
intended to subsequently receive the mechanizing resin. The degree of
penetration of the core resin into the foam layer can be determined as a
function of the thickness of the said foam layer, and of the chemical
nature of the various components used to form this injection resin. In
particular, the viscosity of each of the components used to prepare this
resin is taken into account, with the understanding that the viscosity of
these components is relatively reduced at the start of the reaction that
leads to the formation of the core, but that this viscosity increases
relatively rapidly as soon as the reaction between these various
components is initiated. The limited permeability of the foam layer is
therefore predominant in the first moments of the injection reaction of
the foam intended to form the core.

[0016]Depending on the desired applications, the reinforcing textile
structure of the complex may be prepared in various ways.

[0017]This textile structure may be prepared in particular in the form of
a fibrous layer, based on fibres of glass, carbon or aramid, separate or
combined. These fibres may be organized in the form of a plain or
multidirectional fabric, or in the form of a mat having virtually
isotropic properties.

[0018]The reinforcing textile structure may also consist of an assembly of
a plurality of fibrous layers, combined to optimize the impregnation of
the thermoset mechanizing resin. It may, for example, be a textile
structure such as sold under the Rovicore brand by the Applicant.

[0019]The characteristic foam layer can be joined with the reinforcing
textile structure in various ways. Thus, and preferably, the textile
structure and the foam layer can be joined by stitching/knitting, that is
by a mechanical joining thanks to the binding threads which pass through
the foam layer and the textile structure. This type of joining serves in
particular to ensure good cohesion between the two components of the
complex, and very severely limits the risks of delamination.

[0020]However, the foam layer and the textile structure can be joined in
other ways. Mention can be made in particular of joining by needling,
whereby certain fibres of the reinforcing fibrous structure are displaced
to penetrate into the characteristic foam layer. These two layers can
also be joined by bonding, while nevertheless ensuring that this bonding
is not sealed, in order to prevent the creation of a zone of sudden
changes in mechanical properties, a source of embrittlement. This bonding
can therefore be obtained in a non-uniform manner by the presence of an
openwork adhesive film, or even by the distribution of bonding points.
These bonding points must be sufficiently close to firmly join the
reinforcing textile structure with the foam layer, but they must not be
too close, in order to facilitate the flow of the various resins, and to
prevent the creation of accumulation zones.

[0021]In practice, the characteristic foam layer is selected for its
properties of compatibility with the injection resin. Thus, in the
preferable case of the injection of a polyurethane based core, the foam
and its properties are also selected from the same material.

[0022]Advantageously, in certain circumstances, it is possible to
incorporate in the complex, a film inserted between the foam layer and
the reinforcing layer. Such a film thereby ensures a certain seal between
the open cell foam and the textile reinforcement in the case in which the
penetration of the core is excessive, and in particular close to the
injection points. The possibility of the foam of the core being mixed
with the reinforcing mechanizing resin is therefore avoided. This film is
advantageously made from a material that is degraded or dissolved during
the injection reactions of the mechanizing resin. A material can be
selected in particular that is degraded by the styrene frequently present
in the mechanizing resins. It is in fact preferable for the film to
disintegrate, to at least partially disappear, and no longer remain in
the state of a film in the final part, to avoid causing the appearance of
embrittlement zones detrimental to the solidity of the composite part.
This disintegration is facilitated by the fact that the film is
perforated by the stitching thread binding the layers of the complex.
This disintegration can be further improved in the case in which the film
has specific preperforations, being added to the perforations made by the
stitching threads.

[0023]In practice, the complex according to the invention can be used by
an advantageous method, because it serves to do away with the operations
of sanding of a prefabricated core.

[0024]Thus, such a method comprises the following steps: [0025]placement
in a mould of a complex comprising the textile reinforcing structure
combined with an open cell foam layer; [0026]injection into the mould of
the components reacting to produce a resin forming the core and coming
into contact with the open cell foam layer; [0027]impregnation of the
textile reinforcing structure by injecting a mechanizing resin.

[0028]In other words, contrary to the prior art methods in which the core
is prefabricated, and then sanded to have a surface texture permitting
the bonding of the reinforcement, the method according to the invention
produces the bonding of the reinforcement directly during the injection
of the core resin. It is by the partial penetration of this core resin
into the open cell foam layer that the anchoring of the reinforcement
takes place, because the latter is mechanically joined to this open cell
foam layer.

[0029]In practice, the injection of the mechanizing resin into this
textile reinforcement can take place in the same mould, directly after
injecting the components forming the foam of the core.

[0030]It is also possible to carry out this injection of mechanizing resin
in a different mould from the one in which the core has been formed.
Thus, in this configuration, the steps of preparation of the core with
bonding of the reinforcement is separated from the step of injecting and
curing the mechanizing resin in the reinforcement. In the case in which
these two operations take place in different operating conditions in
terms of time and temperature, it is thereby possible to optimize the
fabrication process.

[0031]In certain cases, it is also possible, between the formation of the
core and the injection of the mechanizing resin, to open tie mould to
place supplementary layers above the reinforcing layer. Such
supplementary layers may be appearance layers, such as layers of Gelcoat
type polyester resin, additional reinforcing layers, or plastic or metal
inserts.

[0032]The composite parts made in the method can easily be identified,
insofar as the core resin partially penetrates into the open cell foam
layer of the mechanically reinforcing complex.

[0033]In practice, the invention therefore serves to produce parts whereof
the reinforcing complex is joined to the core directly during the core
injection operation. In certain cases, the reinforcing complex may also
be arranged in the form of a preshaped cutout, or in the form of a cutout
stitched to form a bag into which the core foam is injected, with
maintenance of the shape inside the mould as required.

BRIEF DESCRIPTION OF THE FIGURES

[0034]The manner in which the invention is implemented, and the advantages
thereof, will clearly appear from the description of the embodiments that
follow, in conjunction with the appended figures in which:

[0035]FIG. 1 is a brief perspective view of a composite part incorporating
the complex according to the invention, shown in a partially cutaway
view;

[0036]FIG. 2 shows a cross section of the part of FIG. 1;

[0037]FIG. 3 shows a cross section of a complex prepared according to an
exemplary embodiment;

[0038]FIGS. 4 to 8 show cross sections of the mould in which the steps of
the inventive method are implemented.

MANNER FOR IMPLEMENTING THE INVENTION

[0039]FIG. 1 shows a composite part (1), including a core (2) associated
with the reinforcing complex (3).

[0040]According to the invention, this reinforcing complex (3) comprises
an open cell foam layer (4), combined with a reinforcing textile
structure (5). The foam layer (4) and the reinforcing textile structure
(5) are joined by stitching/knitting using binding threads (6).

[0041]Although it is not limited to this type of particular application,
the invention has an advantage during the production of composite parts
including a core (2) prepared by the injection of components reacting to
form a polyurethane foam. In this case, the foam forming the
characteristic layer (4) coming into contact with this core (2) is also
preferably based on polyurethane.

[0042]The thickness of the foam layer (4) may be variable, and determined
according to the material used to form the core (2), particularly their
viscosity. This thickness may typically range from 1 to 10 mm. Similarly,
the density of the foam (4) may be variable, conditioning the rate of
penetration of the core injection resin. This density may typically be
between 20 and 250 g/l. In practice, the size and shape of the cells
employed may be adapted to the method and to the matrix used.

[0043]By way of example, the complex (3) shown in FIGS. 1 and 2 may
comprise a polyurethane foam layer having a density of 30 kg/m3, and
a thickness of 3 mm, and hence an area density of 90 g/m2.

[0044]The complex of the invention also comprises a reinforcing layer (5)
which, in the example shown in FIGS. 1 and 2, is a two-directional fabric
based on high toughness yarns and typically glass yams. Many alternative
embodiments can be provided in terms of this reinforcing layer (5)
particularly by using unidirectional reinforcements, or even glass fibre
mats.

[0045]By way of example, the foam layer mentioned previously may be
combined with a glass fibre mat, using fibres having an average length of
50 mm to form a mat having a mass of 300 g/m2. This mat may be
joined by stitching/knitting using synthetic yarns in particular.

[0046]In the embodiment shown in FIG. 3, the reinforcing textile structure
(10) may consist of the assembly of a plurality of layers. Thus, two
actual reinforcing layers (11,13) may be separated by an intermediate
layer (12) prepared based on synthetic yarns having a degree of curl, and
therefore allowing the flow of the thermoset mechanizing resin. The
reinforcing layer (13) may receive a voile (15) on its outer face. This
voile serves to provide an overall more uniform surface texture, and to
mask the corrugations due to the reinforcing texture (13). This
appearance voile (15) may be joined to the complex by stitching, as shown
in FIG. 3. It may also be joined in various ways, and for example by
bonding or needling.

[0047]In an embodiment not shown, the complex according to the invention
may comprise a film inserted between the open cell foam layer and the
textile reinforcement. Such a film serves to prevent excessive migration
of the core foam through the open cell foam, a migration that would
penetrate the textile reinforcing layer. Such a film may be of various
types, insofar as it has a certain chemical compatibility with the
various materials of the resins that it is liable to contact. Good
results have been obtained by using polyurethane films, typically a few
tens of microns thick. This film is sandwiched between the various
elements of the complex, and held with respect to said elements by the
stitching thread passing through it. The fineness of the stitching holes
and the presence of the stitching thread do not excessively affect the
tightness of this film, and facilitates its disintegration by the
components of the mechanizing resin.

[0048]The reinforcement according to the invention can be used by the
method described in FIGS. 4 to 8.

[0049]Thus, in a first step, the complex (3) according to the invention is
placed in a mould (20), to line the walls thereof. The placement may, for
example, be carried out using a layer of adhesive materials sprayed on
the walls of the mould (20). After lining the mould (20), the mould is
closed to confine a closed space (21) into which, as shown in FIG. 5, the
chemical components (22, 23) are injected of the polyol and isocyanate
type which, reacting with one another, formed the polyurethane foam (24)
constituting the core material of the future part. During this reaction,
an expansion takes place, completely filling the internal space (21), as
shown in FIG. 6. When it comes into contact with the open cell foam layer
(4) of the reinforcing complex (3), the polyurethane foam of the core (2)
partially penetrates into this layer, and thereby effectively anchors the
complex to the core.

[0050]Subsequently, it is possible to carry out a second injection step,
for the penetration of the mechanizing resin into the mould (20) to
impregnate the textile reinforcement (5) of the characteristic complex.

[0051]However, in the alternative shown in FIG. 7, the core (2) combined
with the complex (3) can be extracted from the mould. This combination
(26) is easily handled insofar as the reinforcement (5) is firmly
anchored to the core (2) thanks to its open cell foam layer (4). This
combination can thereby, as shown in FIG. 8, be placed in a mould (30)
dedicated to the injection of the mechanizing resin, typically based on
polyester, which is injected according to specific operating conditions.
Thus, the mould for this injection may comprise a lid (32) formed of a
flexible membrane, allowing the application of a downward pressure or
depression (33) causing the resin to defuse from a smaller number of
injection points.

[0052]The opening of the mould (20) and the subsequent transfer of the
part (26) that it contains to another mould, serves to partially relieve
the mechanical stresses imposed on the reinforcing textile (5), and in
particular to facilitate the subsequent diffusion of the mechanizing
resin. Depending on the applications, it is also possible to deposit
additional layers, in particular of "Gelcoat" on the textile
reinforcement (5), before injection of the mechanizing resin (31).

[0053]It appears from the above that the complex according to the
invention has many advantages, and particularly the advantage of allowing
the production of reinforced injected parts in a single step before
impregnation of the reinforcement, while preserving excellent properties
of resistance to delamination by punching.